The present invention relates to an image forming apparatus, such as a cleanerless color laser printer, configured to collect and reuse a developing agent.
In a color laser printer, a color image as obtained by forming an electrostatic latent image on a photoconductor drum, applying developing agents of a plurality of colors to the photoconductor drum with developing rollers to form developing agent images, and then sequentially transferring the developing agent images onto a transfer target medium, such as recording paper or an intermediate transfer belt. During transfer of the developing agent images in such a color laser printer, so-called reverse transfer sometimes occurs. Reverse transfer is a phenomenon that part of the developing agent already transferred onto the transfer target medium is transferred from the transfer target medium onto the photoconductor drum. Occurrence of reverse transfer leads to a problem that the reversely transferred developing agent is mixed with a developing agent of a color to be originally transferred from the photoconductor drum at the next image formation, which results in color mixture and thereby a deteriorated quality of a color image to be formed.
To prevent such a problem, a technique has been presented, in which a property that reverse transfer depends on the ratio (the coverage) of a surface area of the developing agent covered with an outer additive to a surface area of developing agent particles is utilized. Specifically, color mixture due to reverse transfer is prevented in order to obtain an image without undesirable changes in color, by appropriately adjusting the ratio of a surface area of spherical developing agent particles covered with an outer additive to a surface area of the spherical developing agent particles, or appropriately adjusting the shapes of spherical developing agent particles (the deviation from spheres and the unevenness of the particle surfaces).
An example of such a technique is disclosed in the Publication of Japanese Patent No. 3248047.